Automatic defrosting systems for twotemperature refrigerators



0 1955 F. L. TARLETON AUTOMATIC DEFROSTING SYSTEMS FOR TWO-TEMPERATUREREFRIGERATORS Filed Aug. 15, 1953 115V AC. POWER SOURCE -INVENTORFrederic L. Iar/efon United States Patent AUTOMATIC DEFROSTIN G SYSTEMSFOR TWO- TEMPERATURE REFRIGERATORS Frederic L. Tarleton, Oak Park, Ill.,assignor to Gencrai Electric Company, a corporation of New YorkApplication August 13, 1953, Serial No. 374,047 Claims. (Cl. 62-4) Thepresent invention relates to two-temperature refrigerators and moreparticularly to automatic defrosting systems therefor.

A conventional refrigerator of the two-temperature type comprises anupstanding heat insulated cabinet defining separate upper and lower foodstorage compart' ments, and a refrigeration system of thecompressorcondenser-evaporator type including a low-temperatureevaporator operatively associated with the upper compartment to cool itto a temperature below the freezing point (usually about 0 F.) and ahigh-temperature evaporator arranged in the upper portion of the lowercompartment to cool it to a temperature above the freezing point(usually about 35 F.). Since the high-temperature evaporator is incontact with the convection currents of moist air circulated in thelower compartment frost accumulates thereon, whereby thehigh-temperature evaporator must be periodically defrosted to maintain asatisfactory operating condition. In order to achieve this objective,various defrosting schemes have been proposed that normally proceed onthe basis of supplying heat to the high-temperature evaporator under thecontrol of timing mechanism, counting mechanism, etc.

While these defrosting arrangements are reasonably satisfactory inoperation, they are considerably more expensive to manufacture than isdesirable.

Accordingly, it is a general object of the present. invention to providea two-temperature refrigerator of the character noted, that incorporatesan improved refrigeration system, whereby the high-temperatureevaporator arranged in the lower or high-temperature food storagecompartment is automatically defrosted at the conclusion of each oncycle of the compressor as a result of the inherent operatingcharacteristic of the refrigeration apparatus, and without the provisionof auxiliary control mechanism.

Another object of the invention is to provide a two temperaturerefrigerator of the character described, in which a continuous andunvalved conduit is arranged from the condenser back to the compressorand including in series relation the high-temperature evaporator in theform of a restricted evaporator tube and the low-temperature evaporatorin the form of an unrestricted evaporator tube, whereby the gaseousrefrigerant accumulating in the high-temperature evaporator during eachoff cycle-of the compressor eifects flushing ofthe liquid refrigeranttherefrom into the low-temperature evaporator so that the temperature ofthe high-temperature evaporator rises above the freezing point beforethe next on cycle of the compressor in order to defrost thehightemperature evaporator following each on cycle of the compressor.

A further object of the invention is to provide a twotemperaturerefrigerator ofthe character described, and further including openheat-transfer structure arranged in the upper portion of the lower orhigh-temperature compartment in good heat exchangerelation with both thehi git-temperature evaporator and the convection currents of aircirculated in the lower or high-temperature compartment, whereby theheat-transfer structure brings about cooling in the lower orhigh-temperature compartment during each on cycle of the compressor andbrings about defrosting of the high-temperature evaporator during eachofi cycle of the compressor.

Further features of the invention pertain to the particular arrangementof the elements of the two-temperature refrigerator and therefrigeration apparatus, whereby the above-outline and additionaloperating features thcreof are attained.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a two-temperature refrigeratorprovided with refrigeration apparatus incorporating an automaticdefrosting arrangement and embodying the present invention; and

Fig. 2 is a fragmentary perspective view of the hightemperatureevaporator that is arranged in the upper portion of the lower orhigh-temperature food storage compartment of the refrigerator shown inFig. 1.

Referring now to Fig. 1 of the drawing, the twotemperature refrigerator10 there illustrated and embodying the features of the present inventioncomprises an upstanding heat insulated cabinet 11 defining separateupper and lower food storage compartments 12 and 13, as well as amachinery compartment 14disposed below the lower food storagecompartment 13. The upper compartment 12 constitutes a low-temperaturecompartment and is defined by a sheet metal liner 15 having a frontccess opening, and the lower compartment 13 constitutes ahigh-temperature compartment and is defined by a sheet metal liner 16having a front access opening; and the cabinet 11 carries a heatinsulated main front door 17 for closing the front openings mentioned inorder to prevent the admission of heat and air thereinto, the front door17 being pivoted to the cabinet 11 along one upstanding marginal edgethereof in a conventional manner, not shown. Also the front accessopening into the upper compartment 12 is provided with an auxiliaryfront door 18, hinged adjacent to the lower edge thereof, and servingthe general purpose of closing the upper compartment 12 against theadmission of air thereinto when the main front door 17 is open to renderaccessible the lower compartment 13. Of course, the auxiliary front door18 may be opened, when the main front door 17 occupies its openposition, so as to render accessible the upper compartment 12. Finally,the front of the machinery compartment 14 is closed by a removable frontpanel 19 that is normally disposed substantially flush with the mainfront door 17 so as to lend a smooth and unbroken appearance to thefront of the refrigerator 10.

The refrigerator 10 incorporates refrigeration apparatus of thecompressor-condenser-evaporator type and. including a composite electricmotor-compressor unit 20 and a condenser 21 of the fan-cooled type(provided with an electric operating motor), all disposed in themachineiy compartment 14, as well as a high-temperature evaporator 22disposed in the upper portion of the lower compartment 13, and alow-temperature evaporator 23 arranged in heat exchange relation withthe upper compartment 12. Alternatively the condenser 21 may be of thenatural draft stack type and disposed at the rear of the cabinet 11. Thecompressor, not shown, of the motorcompressor unit 263 is provided withsuction and discharge ports and is operative to compress. expandedgaseous refrigerant, the compressed gaseous refrigerant being conductedfrom the discharge port of the compressor, not shown, via a connection24 into the upper inlet of the condenser 21 that may comprise a seriesof serpentine condenser tubing provided with suitable heat-transferstructure. The motor-compressor unit 20 and the condenser 21 togetherconstitute a refrigerant liquifying unit; and a continuous and unvalvedconduit is arranged from the lower outlet of the condenser 21 to thesuction port of the compressor, not shown, of the motor-compressor unit20. This continuous and unvalved conduit includes in series relation acapillary tube 25, the high-temperature evaporator 22, thelow-temperature evaporator 23 and a suction tube 26. Thehigh-temperature evaporator 22 essentially comprises a section ofevaporator tube 27 of relatively small inside diameter; and thelow-temperature evaporator 23 essentially comprises a section ofevaporator tube 28 having a larger inside diameter as compared with thetube 27. For the purpose of differentiation, the evaporator tube 27 willbe referred to as the restricted tube and the evaporator tube 28 will bereferred to as the unrestricted tube, in view of the dimensionaldifferences thereof. The inner end of the capillary tube 25 is connectedto the outlet of the condenser 21; the outer end of the capillary tube25 is connected to the inner end of the evaporator tube 27; the outerend of the evaporator tube 27 is connected to the inner end of theevaporator tube 28; the outer end of the evaporator tube 28 is connectedto an accumulator 29; the inner end of the suction tube 26 is connectedto the accumulator 29; and the outer end of the suction tube 26 isconnected to the suction port of the compressor, not shown, of themotor-compressor unit 20.

The high-temperature evaporator 22 may comprise a relativelyconventional fin and tube construction, or a composite sinuousstructure; as illustrated in Fig. 2, the latter construction includes,in addition to the evaporator tube 27, open heat-transfer structure 30formed of metal, to which tube 27 is suitably secured in goodheat-transfer relation. In any event, the evaporator 22 Willadvantageously have one or more brackets or legs 31 facilitating thesupport of the high-temperature evaporator 22 upon a wall of the lowercompartment 13 in spaced relation therewith.

As shown in Fig. l, the cabinet 11 has a forwardly tapered heatinsulated dividing wall 32 disposed between the upper and lowercompartments 12 and 13, whereby the upper liner 15 is provided with asubstantially horizontal bottom wall 33 and the lower liner 16 isprovided with a downwardly and rearwardly sloping top wall 34. Finally,the high-temperature evaporator 22 is secured to the top wall 34 by thelegs 31, as previously noted. The high-temperature evaporator 22 isdisposed substantially parallel to the top wall 34 and in spacedrelation therebelow so that it is disposed in the moist convectioncurrents of air circulated in the lower compartment 13, as indicated bythe broken lines 35. Accordingly, the hightemperature evaporator 22slopes downwardly and to the rear in the upper portion of the lowercompartment 13 to facilitate the draining of condensate therefromincident to defrosting thereof, as explained more fully hereinafter; anda laterally extending trough 36 is operatively associated with the lowerrear end of the high-temperature evaporator 22, for the purpose ofreceiving the drippings, the trough 36 communicating with a drip pan 37disposed therebelow in the rear upper portion of the lower compartment13 and carried by the rear portion of an open wire-work shelf 38'supported therein.

Finally, the refrigerator is provided With a control system including asource of electric power supply of 115-volt single-phase A. C., as wellas a thermal control switch 38. The thermal control switch 38 includes aresilient bellows 39 connected by a tube 40 to a temperature responsivebulb 41 arranged in good heat exchange relation with the side wall ofthe lower liner 16, whereby the thermal control switch 38 is governed inresponse to the temperature of the lower compartment 13. Also, thethermal control switch 38 may have a contact bridging member 42 inseries circuit relation with the source of power supply and the electricmotor, not shown, of the motor-compressor unit 20. Finally, the thermalcontrol switch 38 has a manual adjustment indicated at 43, foradjustment of the control temperature.

In a typical two-temperature refrigerator, the capillary tube 25 mayhave an inside diameter in the range of 0.022" to 0.040"; the evaporatortube 27 may have an inside diameter of about 0.187"; and the evaporatortube 28 may have an inside diameter of about 0.375". The inside diameterof the suction tube 26 is not critical, it being well understood in theart that one of the factors of its selection is the passage ofrefrigerant vapor from the accumulator to the compressor with as low apressure drop as is consistent with practical manufacturing and economicconsiderations. The inside diameter of the evaporator tube 27 is, ofcourse, predicated upon the fundamental consideration that during theoff period of the compressor, heat transfer from the air in thecompartment 13 to the evaporator tube 27 will quickly vaporize someliquid refrigerant therein, and that the vaporized refrigerant will, inpercolator fashion, quickly flush the liquid refrigerant out of theevaporator tube 27 and into the evaporator tube 28. This enables theheat of the contents of the compartment 13 during the off period of thecompressor to melt any frost which may have accumulated on theevaporator 22 during the preceding on period. A tube diameter such asgiven above for the evaporator tube 27 insures that the surface tensionof the liquid refrigerant is sufiicient to resist the penetration of theliquid refrigerant by the refrigerant vapor bubbles pressingthereagainst, and these refrigerant vapor bubbles therefore efiicientlydrive the liquid refrigerant before them.

In the two-temperature refrigerator 10, there is a further expansion ofthe liquid refrigerant as it passes into the evaporator tube 28. Theabove noted size difference between the evaporator tubes 27 and 28provides the required expansion of the liquid refrigerant within theevaporator tube 28 for the desired heat absorption from the compartment12.

Alternatively, such expansion of the liquid refrigerant may be achieved,without the above-described differential between the cross-sectionalareas of the evaporator tubes 27 and 28, by installing a plug, notshown, at the junction of the evaporator tubes 27 and 28, this plughaving a restricted orifice communicating between the evaporator tubes27 and 28, whereby effectively the above noted relationship between theevaporator 22 and the evaporator 23 may be achieved.

In the operation of the refrigerator 10, the upper low temperaturecompartment 12 is normally maintained at about 0 F., and the lowerhigh-temperature compartment 13 is normally maintained at about 35 E;which temperature differential is maintained by the normal operation ofthe refrigeration apparatus since the evaporator tube 27 accommodatesexpansion of a portion of the liquid refrigerant therein, and furtherexpansion of the liquid refrigerant is accommodated in the evaporatortube 28. More particularly, when the temperature of the lowercompartment 13 rises slightly above the control temperature, of about 35F., normally set to govern the thermal control switch 38, this controlswitch is operated into its closed position so that operation of themotor-compressor unit 20 is initiated. Expanded gaseous refrigerant isdrawn from the suction tube 26 into the compressor, not shown, of themotor-compressor unit 20 and compressed and discharged therefrom 24 intothe condenser 21. The compressed gaseous refrigerant is liquified in thecondenser 21 and immediately passes therefrom via the capillary tube 25into the restricted evaporator tube 27; the capillary tube 25, becauseof its extremely small inside diameter, accommodating substantially noexpansion of the liquid refrigerant therein. The liquid refrigerant isnot fully expanded in the restricted evaporator tube 27 whereby thedischarge from the reimmense stricted evaporator tube 27 into theunrestricted evaporator tube28 contains quantities .of liquidrefrigerant.

The cooling of the high-temperature evaporator '22which takes place byreason of the refrigerantexpansion therein suitably cools the convectioncurrents of air circulated in the lower or high-temperature compartment13-. The liquid refrigerant entering "the unrestricted evaporator tube28 isfurther expanded, the pressure intheunrestricted evaporatortubel 28beingdetermined entirely*by the pressure in the suction tube 26, that,in" tu'rn,is established directly by 'the suction of the compressor, not

shown, of the motor-compressor unit whereby the cooling ofthelow-temperatu-re evaporator 23 resulting from such expansionprovidesthedesired cooling of the upper or low-temperature compartment 12. Byvirtue of the arrangement of the differential pressures automaticallyestablished in the restricted evaporator tube'27 and in theunrestrictedevaporatortubels, the lower compartment 13 is cooledto a temperature ofabout F.

when the upper compartmentIZ is cooled to about a temperature of 0 F;whereby at this time the bulb 41 is governedto effect operation of thethermal control switch 38 into its open circuit positionin order toarrest operation of the electric 'motor of themotor-compressor unit 2t).In the oncycle ofthe motor-compressor unit 20, the convection currents'ofair circulated in the lower compartment 13 effectthe transfer of"heat to "the hightemperature evaporator 22, -while heat from the upperliner 15 is directlytransferred to the low temperature evaporator 23.

During the off cycle of the motor-compressor unit 20, the convectioncurrents of air circulated'in the lower compartment 13 continue totransfer heat'to thehightemperature evaporator 22; whereby some of theliquid refrigerant in the restricted evaporator tube 27 isgasified sothat the expanded gaseous refrigerant therein flushes the liquidrefrigerant therein forwardlytherefrom into the unrestricted evaporatortube 28; this action in the restricted evaporator tube 27 beinganalogous to that involved in the operation of a normal percolator;whereby a small amount of gaseous refrigerant sweeps forwardly a largeamount of Iiquidrefrigerant. This arrangementreduces the latent heat inthe high-temperature evaporator 22 so that shortly thereafter thecontinued transfer of heat thereto causes the temperature thereof torise above the freezingpoint; whereby the high-temperature evaporator 22is defrosted, thecondensate draining downwardly thereonand falling intothetrough 36 and-then running into the drip pan 37. After this completedefrosting of the high-temperature evaporator 22 in the off cycle of themotor-compressor unit 20, the thermal control switch 38 is subsequentlygoverned in order again to initiate 7 operation of the motor-compressorunit 20. On the other hand, there is very little heating-of the uppercompartment 12 during the off cycle of the motor-compressor unit 2d;whereby the temperature thereinis maintained substantially constant, atabout 0 F.

In view of the above, it will beunderstood that following each on cycleof the motor-compressoriunit 20, the high-temperature evaporator 22 isautomatically defrosted by virtue of the inherent operatingcharacteristic of the refrigeration apparatus; whereby it is unnecessaryto incorporate in the refrigerator 10 any auxiliary control or heatingapparatus to bring about the necessary defrosting. of thehigh-temperature evaporator 22. The defrosting operation of thehigh-temperature evaporator 22 takes place automatically, as describedabove, by virtue of the fact that the restricted evaporator tube 27 isconnected at the inlet end thereof to the exceedingly restrictedcapillary tube 25 and is connected at the outlet end thereof to theunrestricted evaporator tube 28; whereby the small heating of thehigh-temperature evaporator 22 in the off cycle ofthe motor-compressorunit 2 0eifects the limited gasification of the liquid refrigerant intherestricted evaporatortube'27 so thatthe mass of liquid 6 refrigeranttherein is swept forwardly therefrom due to the percolator-like action,previously described.

In view of the foregoing, it is apparent that there has been provided atwo-temperature refrigerator incorporating refrigeration apparatus thatis so constructed and arranged that automatic defrosting of thehigh-temperature evaporator arranged in the upper portion of the loweror high-temperature food storage compartmentthereof takes place in eachoff cycle of the motor-compressor unit and before the next on cyclethereof; which defrosting arrangement is entirely automatic anddependent altogether upon the inherent operating characteristic of therefrigerator apparatus, and requires no supervision, adjustment orattention on the part of the user of the refrigerator.

While the preferred embodiment of the invention has been disclosed asbeing incorporated in the two-temperature refrigerator 10, having theupper compartment 12 provided with the unrestricted evaporator 23 andthe lower compartment 13 provided with the restricted evaporator 1:cabinet 11.

While there has been described what is atpresent considered to be thepreferred embodiment of the invention, it will be understood thatvarious modificationsmay be made therein, and it is intended tocover inthe appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In a refrigerator including an upstanding heatinsulated cabinetdefining separate first and .secondfood storage compartments, acompressor operative to compress expanded gaseous refrigerant, acondensenand a connection for conducting compressed gaseous refrigerantfrom said compressor to said condenser; the combination comprising acontinuous conduit from said condenser back to said compressor andincluding in series relation in the order named a capillary tube and afirst restricted evaporator tube and a second unrestricted evaporatortube and an unrestricted suction tube, whereby said first restrictedevaporator tube is located between said capillary tube and said secondunrestricted evaporator tube in said conduit, said first evaporator tubebeing arranged in the upper portion of said first compartment and saidsecond evaporator tube being arranged in heat-exchange relation withsaid second compartment, said capillary tube accommodating substantiallyno expansion of the liquid refrigerant therein, said first evaporatortube accommodating predetermined expansion of the liquid refrigeranttherein so as to cool said first compartment to a temperature above thefreezing point, said second evaporator tube accommodating furtherexpansion of the liquid refrigerant therein so as to cool said secondcompartment to a temperature below the freezing point, thermalresponsive means controlled by the temperature of said first compartmentfor operating said compressor between off and on cycles, and openheat-transfer structure arranged in the upper portion of said firstcompartment in good heat exchange relation. with both said firstevaporator tube and the convection currents of air circulated in saidfirst compartment, the gaseous refrigerant accumulating in said firstevaporator tube during each off cycle of said compressor as aconsequence of the heat transferred thereto from said structure and as aresult of said location of said first evaporator tube in said conduiteffecting flushing of the liquid refrigerant therefrom into said secondevaporator tube so that the temperature of said first evaporator tuberises above the freezing point before the next on cycle of saidcompressor, whereby said first evaporator tube and said structure aredefrosted following each on cycle of said compressor.

2. Therefrigerator combination set forth in claim 1, wherein thecross-sectional area of said-first evaporator tube is about 20 to 70times greater than that of said capillary tube, and the cross-sectionalarea of said second evaporator tube at its junction with said firstevaporator tube is substantially greater than that of said firstevaporator tube.

3. The refrigerator combination set forth in claim 1, wherein saidcabinet also defines a separate machinery compartment disposed belowsaid food storage compartments, and said compressor and said condenserare disposed in said machinery compartment.

4. The refrigerator combination set forth in claim 1, wherein said firstand second food storage compartments are provided with respective firstand second sheet metal liners, said first evaporator tube and saidstructure are arranged interiorly of said first liner and substantiallyout of contact therewith, and said second evaporator tube is arrangedexteriorly of said second liner and in contact and good heat exchangerelation therewith.

5. The refrigerator combination set forth in claim 1, wherein saidthermal responsive means operates said compressor between off and 011cycles about two to three times per hour.

6. In a refrigerator including an upstanding heatinsulated cabinetdefining separate upper and lower food storage compartments havingcorresponding front openings, a heat-insulated door for closing saidfront openings, a compressor operative to compress expanded gaseousrefrigerant, a condenser, and a connection for conducting compressedgaseous refrigerant from said compressor to said condenser; thecombination comprising a continuous and unvalved conduit from saidcondenser back to said compressor and including in series relation inthe order named a capillary tube and a first restricted evaporator tubeand a second unrestricted evaporator tube and an unrestricted suctiontube, whereby said first restricted evaporator tube is located betweensaid capillary tube and said second unrestricted evaporator tube in saidconduit, said first evaporator tube being arranged in the upper portionof said lower compartment and said second evaporator tube being arrangedin heat-exchange relation with said upper compartment, said capillarytube accommodating substantially no expansion of the liquid refrigeranttherein, said first evaporator tube accommodating sufficient expansionof the liquid refrigerant therein to cool said lower compartment to atemperature above the freezing point, said second evaporator tubeaccomodating further expansion of the liquid refrigerant therein so asto cool said upper compartment to a temperature below the freezingpoint, thermal responsive means controlled by the temperature of saidlower compartment for operating said compressor between off and oncycles, and open heat-transfer structure arranged in the upper portionof said lower compartment in good heatexchange relation with both saidfirst evaporator tube and the convection currents of air circulated insaid lower compartment, the gaseous refrigerant accumulating in saidfirst evaporator tube during each cycle of said compressor as aconsequence of the heat transferred thereto from said structure and as aresult of said location of said first evaporator tube in said conduiteffecting flushing of the liquid refrigerant therefrom into said secondevaporator tube so that the temperature of said first evaporator tuberises above the freezing point before the next on cycle of saidcompressor, whereby said first evaporator tube and said structure aredefrosted following each on cycle of said compressor, said structuresloping downwardly toward the rear of said lower compartment tofacilitate the collection of drippings therefrom incident to defrostingthereof.

' 7 The refrigerator combination set forth in claim 6, wherein saidcabinet includes a forwardly tapered dividing wall disposed between saidupper and lower compartments and providing said upper compartment with asubstantially horizontal bottom wall and providing said lowercompartment with a downwardly and rearwardly sloping top wall.

8. In a refrigerator including a heat-insulated cabinet defining astorage compartment, a compressor operative to compress expanded gaseousrefrigerant, a condenser, and a connection for conducting compressedgaseous refrigerant from said compressor to said condenser; thecombination comprising an evaporator arranged in the upper portion ofsaid compartment and provided with a refrigerant passage for circulationof refrigerant therethrough, an accumulator, first means defining ahighly restricted communication between said condenser and the inlet ofsaid refrigerant passage to conduct liquid refrigerant thereto, wherebyduring periods of operation of said compressor said evaporator providessubstantially continuous expansion and evaporation of liquid refrigeranttherein to lower the temperature thereof sufficiently below the freezingpoint of water to maintain said compartment at a temperature in adesired range above said freezing point, second means defining amoderately restricted communication between the outlet of saidrefrigerant passage and said accumulator, third means defining anunrestricted passage from said accumulator to said compressor for thereturn of expanded gaseous refrigerant to said compressor, and thermalresponsive means controlled by a predetermined variation in thetemperature of said cabinet for operating said compressor between 01fand on cycles; said evaporator including an open heat-transfer structurein good heat exchange relation with said refrigerant passage and theconvection currents of air in said compartment, and the cross sectionalarea of said refrigerant passage being such that upon heat transfer fromthe air in said compartment to said refrigerant passage during an offperiod of said compressor vaporization of liquid refrigerant in saidrefrigerant passage will be effective as a result of the location ofsaid refrigerant passage between said first means and said second meansquickly to flush remaining liquid refrigerant from said refrigerantpassage into said accumulator to reduce the latent heat in saidevaporator and thereby permit the temperature of said evaporator to riseabove the freezing point of water before the next 'on period of saidcompressor.

9. The refrigerator combination set forth in claim 8, wherein said firstmeans defining said highly restricted communication between saidcondenser and said evaporator consists essentially of a capillary tube,and said second means defining said moderately restricted communicationbetween said evaporator and said accumulator consists essentially of arestricted evaporator tube forming at least a part of said refrigerantpassage and being many times larger in inside diameter than saidcapillary tube, and said third means defining said unrestrictedcommunication between said accumulator and said compressor consistsessentially of a relatively large inside diameter suction tube.

10. The refrigerator combination set forth in claim 9, wherein saidcapillary tube and said suction tube are arranged in heat exchangerelation with each other.

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